Comet Ikeya-Zhang rises for the NAM     

David Asher  Mark Bailey  Apostolos Christou  John McFarland  Mark Muir  Paul Rafferty 《Astronomy& Geophysics》2002,43(2):2.19-2.21

A possible naked-eye comet that may have been important in early cometary theory is announced by D J Asher , M E Bailey , A Christou , J McFarland , M F Muir and P P Rafferty .
Early indications sugest that Comet C/2002 (Ikeya-Zhang), discovered on 1 February 2002, may brighten to naked-eye visibility in late March 2002. It has also been suggested that it may be identical to one of the brighter comets of the 16th or 17th centuries, namely C/1532 R1 or C/1661 C1. The first of these, observed for more than 100 days towards the end of 1532, played an important role in the development of cometary theory. The second, although identified by Halley as having an orbit similar to that of the comet C/1532 R1, was not seen on its predicted return in 1788/1789 and so was presumably unrelated. Here we present long-term orbital integrations of C/2002 C1 which suggest that it orginated from the Oort cloud, and will be ejected again, within ˜0.3 Myr. There is a chance of 10–20% that it will end its life by falling into the Sun during a Halley-type phase of cometary evolution. The discovery of Ikeya-Zhang so closeto perigee by two amateur astonomers highlights the need for surveys covering both hemispheres to discover long-period and intermediate-period comets on Earth-crossing orbits.  相似文献   

Luxury Tourism and Regional Economic Development in Mexico   总被引：1，自引：0，他引：1  

Ludger Brenner  Adrin Guillermo Aguilar 《The Professional geographer》2002,54(4):500-520

This article argues that little attention has been paid to the territorial and socioeconomic impact of consumer–service globalization on Third World countries. It specifically examines the economic role of tourism in Mexico and its limited effect on the country's regional development. Despite governmental support in order to enhance economic growth, currency receipts, and employment, tourism contributes less than 5 percent to the gross domestic product, and the majority of tourism–related jobs are precarious and low–skilled. The promotion of luxury resorts in coastal areas has led to highly concentrated and fast–growing enclaves of mainly foreign investment. However, this strategy has failed to stimulate productive links between tourist centers and their hinterlands and has led to large–scale urbanization characterized by a considerable lack of basic services for the resident population.  相似文献   

Broad-band observations of earthquake-induced rotational ground motions     

Heiner Igel  Alain Cochard  Joachim Wassermann  Asher Flaws †  Ulrich Schreiber  Alex Velikoseltsev  Nguyen Pham Dinh 《Geophysical Journal International》2007,168(1):182-196

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Special Contributions: Pictorial Series of the Manifestations of the Dynamics of the Earth: 5. Kamchatka,Its Early Cartography and Recent Climate Changes     

Kozák  Jan  Brenner  Karel  Čermák  Vladimír 《Studia Geophysica et Geodaetica》2003,47(4):875-886

Studia Geophysica et Geodaetica -  相似文献   

Influence of vegetation change on watershed hydrology: implications for paleoclimatic interpretation of lacustrine δ18O records     

Michael F. Rosenmeier  David A. Hodell  Mark Brenner  Jason H. Curtis  Jonathan B. Martin  Flavio S. Anselmetti  Daniel Ariztegui  Thomas P. Guilderson 《Journal of Paleolimnology》2002,27(1):117-131

Stratigraphic shifts in the oxygen isotopic (¹⁸O) and trace element (Mg and Sr) composition of biogenic carbonate from tropical lake sediment cores are often interpreted as a proxy record of the changing relation between evaporation and precipitation (E/P). Holocene ¹⁸O and Mg and Sr records from Lakes Salpetén and Petén Itzá, Guatemala were apparently affected by drainage basin vegetation changes that influenced watershed hydrology, thereby confounding paleoclimatic interpretations. Oxygen isotope values and trace element concentrations in the two lowland lakes were greatest between ~ 9000 and 6800 ¹⁴C-yr BP, suggesting relatively high E/P, but pollen data indicate moist conditions and extensive forest cover in the early Holocene. The discrepancy between pollen- and geochemically-inferred climate conditions may be reconciled if the high early Holocene ¹⁸O and trace element values were controlled principally by low surface runoff and groundwater flow to the lake, rather than high E/P. Dense forest cover in the early Holocene would have increased evapotranspiration and soil moisture storage, thereby reducing delivery of meteoric water to the lakes. Carbonate ¹⁸O and Mg and Sr decreased between 7200 and 3500 ¹⁴C-yr BP in Lake Salpetén and between 6800 and 5000 ¹⁴C-yr BP in Lake Petén Itzá. This decline coincided with palynologically documented forest loss that may have led to increased surface and groundwater flow to the lakes. In Lake Salpetén, minimum ¹⁸O values (i.e., high lake levels) occurred between 3500 and 1800 ¹⁴C-yr BP. Relatively high lake levels were confirmed by ¹⁴C-dated aquatic gastropods from subaerial soil profiles ~ 1.0–7.5 m above present lake stage. High lake levels were a consequence of lower E/P and/or greater surface runoff and groundwater inflow caused by human-induced deforestation.  相似文献   

A ∼6100 14C yr record of El Niño activity from the Galápagos Islands     

Melanie A. Riedinger  Miriam Steinitz-Kannan  William M. Last  Mark Brenner 《Journal of Paleolimnology》2002,27(1):1-7

Lithostratigrahic and mineralogic analyses of sediments from hypersaline Bainbridge Crater Lake, Galápagos Islands, provide evidence of past El Niño frequency and intensity. Laminated sediments indicate that at least 435 moderate to very strong El Niño events have occurred since 6100 ¹⁴C yr BP (7130 cal yr BP), and that frequency and intensity of events increased at about 3000 ¹⁴C yr BP (3100 cal yr BP). El Niño activity was present between 6100 and 4000 ¹⁴C yr BP (4600 cal yr BP) but infrequent. The Bainbridge record indicates that there has been considerable millennial-scale variability in El Niño since the mid-Holocene.  相似文献   

Numerical analysis of field-scale transport of bromacil     

David Russo  Inbar Tauber-Yasur  Asher Laufer  Bruno Yaron 《Advances in water resources》1998,21(8):1637

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Meteor observations in Japan: new implications for a Taurid meteoroid swarm     

Asher  & Izumi 《Monthly notices of the Royal Astronomical Society》1998,297(1):23-27

Observational evidence is sought that the long-term (10⁴ yr) action of a mean motion resonance with Jupiter can produce structure in a meteoroid stream, concentrating meteoroids in a dense swarm. More specifically, predictions tabulated by Asher & Clube of enhanced meteor and fireball activity from a Taurid Complex swarm in the 7:2 resonance are compared with observational data collected in Japan over several decades. The swarm model was proposed for reasons independent of the observations analysed here, and these newly considered data are shown to be consistent with it. This allows increased confidence in the Taurid swarm theory, and more generally could mean that resonant trapping is a dynamical mechanism affecting a significant amount of meteoroidal material in the inner Solar system.  相似文献   

Fluvial processes and settlement in arid environments     

Prof. Asher P. Schick 《GeoJournal》1979,3(4):351-360

The impact of fluvial geomorphic processes on settlement in deserts is tie d to two conflicting factors: the extreme rarity of geomorphic events on the one hand, and the violence of the geomorphic forces coupled with a minimal resistance to erosion on the other.The unique character of desert floods calls for a careful geomorphic evaluation in the siting of settlements and transportation facilities. On the beneficial sid e, the geomorphic processes involved enable, under some conditions, the local exploitation of floodwaters which percolate in the alluvium of the upper tributaries, as well as the utilization of the hydraulic geometry for estimating discharge characteristics.On a larger scale, human interference often disrupts the delicate quasi-equilbrium between erosion and sedimentation in deserts. Although our poor understanding of many aspects of the mechanism of response makes it difficult to separate the effects from those of climatic changes, enough information is available to document the detrimental effect of inconsiderate management on both the regional and local levels.  相似文献   

Organic chemical characterization of sediment-trap particulates from San Nicolas,Santa Barbara,Santa Monica and San Pedro Basins,California     

P.T. Crisp  S. Brenner  M.I. Venkatesan  E. Ruth  I.R. Kaplan 《Geochimica et cosmochimica acta》1979,43(11):1791-1801

Particulate matter was collected during September–October, 1977, in particle traps suspended 30–60 m above the floor of San Nicolas, Santa Barbara, Santa Monica and San Pedro Basins, off the coast of southern California. The trap particulates were analyzed for C₁₅–C₃₅ hydrocarbons using gas chromatography (GC) and GC-mass spectrometry. Kerogens and humic acids were characterized by H/C, N/C, δ¹³C, δ¹⁵N and δ³⁴S ratios, and by electron-spin resonance. Hydrocarbons arising from fresh and weathered petroleum, marine autochthonous and terrestrial sources were identified. The rates of petroleum deposition during the collection period followed the order: San Nicolas Basin < Santa Barbara Basin ~ Santa Monica Basin < San Pedro Basin, with the largest amount of weathered petroleum being deposited in San Pedro Basin. The rates of petroleum deposition are correlated more strongly with human activities such as shipping, and the discharge of municipal and industrial wastes, than with natural submarine oil seepage. Analyses of kerogens and humic acids indicate that the majority of the organic matter in the trap particulates is of marine origin. The water column overlying Santa Barbara Basin appears to have the highest marine productivity of the four basins studied.  相似文献